1. Technical Field of the Invention
The present invention relates generally to a gas sensor which is installed, for example, in an exhaust system of automotive internal combustion engines to measure a preselected component of exhaust emissions, and more particularly to an improved structure of such a gas sensor which is designed to ensure the stability of electrical connection between contacts and mating parts in the gas sensor.
2. Background Art
There are known gas sensors installed in an exhaust system of automotive internal combustion engines. Japanese Patent First Publication No. 2004-144732 teaches such a type of a gas sensor 9, as illustrated in FIG. 7, designed to measure the concentration of oxygen or nitrogen oxides (NOx) contained in exhaust emissions from the engine.
The gas sensor 9 includes a plate-shaped sensor element 92 responsive to gas to be measured and a porcelain insulator 93 within which the sensor element 92 is retained. The porcelain insulator 93 is fit in a housing 94. A porcelain insulator 95 is disposed above the porcelain insulator 93 to cover a base end 921 (i.e., an upper end, as viewed in the drawing) of the sensor element 92. An air cover 95 is joined to a base end (i.e., an upper end, as viewed in the drawing) of the housing 94 to cover the porcelain insulator 95.
Within the porcelain insulator 95, contacts 97 are disposed in electrical contact with terminals affixed to the sensor element 92. The contacts 97 are joined to leads 98.
The structure of the gas sensor 9, however, has the following drawback.
When the leads 98 are pulled undesirably from outside the gas sensor 9, it will cause the contacts 97 to be also pulled to the base end of the gas sensor 9. In the worst case, the contacts 97 are dislodged out of the porcelain insulator 95, so that they are electrically disconnected from the sensor element 92. Even if the contacts 97 are held firmly within the porcelain insulator 95, they may slide vertically along with the porcelain insulator 95, which results in electrical disconnection of the contacts 97 from the sensor element 92.